SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2016
Segment data [Abstract]
Total interest and dividend income	$ 27,718	$ 20,629	$ 50,293	$ 38,904
Interest expense	3,752	691	6,494	1,411
Net interest income (expense)	23,966	19,938	43,799	37,493
Provision for loan losses	8,649	1,173	9,492	1,959
Non-interest income	92,170	40,901	111,519	57,735
Non-interest expense	66,946	41,790	103,699	71,798
Income before income tax expense	40,541	17,876	42,127	21,471
Total assets	3,985,596	3,071,742	3,985,596	3,071,742	$ 4,006,419
Total deposits	2,872,231	2,220,761	2,872,231	2,220,761	$ 2,430,082
Payments [Member]
Segment data [Abstract]
Total interest and dividend income	3,312	2,633	6,224	4,597
Interest expense	503	54	503	94
Net interest income (expense)	2,809	2,579	5,721	4,503
Provision for loan losses	7,883	953	8,214	1,033
Non-interest income	90,462	39,591	109,487	54,943
Non-interest expense	41,452	25,720	62,324	41,737
Income before income tax expense	43,936	15,497	44,670	16,676
Total assets	74,194	53,020	74,194	53,020
Total deposits	2,606,674	2,014,548	2,606,674	2,014,548
Banking [Member]
Segment data [Abstract]
Total interest and dividend income	12,807	8,949	23,562	17,800
Interest expense	672	316	1,215	569
Net interest income (expense)	12,135	8,633	22,347	17,231
Provision for loan losses	766	220	1,278	926
Non-interest income	1,387	899	2,458	1,955
Non-interest expense	5,958	5,218	11,514	10,646
Income before income tax expense	6,798	4,094	12,013	7,614
Total assets	1,145,054	781,380	1,145,054	781,380
Total deposits	228,805	206,213	228,805	206,213
Corporate Services/Other [Member]
Segment data [Abstract]
Total interest and dividend income	11,599	9,047	20,507	16,507
Interest expense	2,577	321	4,776	748
Net interest income (expense)	9,022	8,726	15,731	15,759
Provision for loan losses	0	0	0	0
Non-interest income	321	411	(426)	837
Non-interest expense	19,536	10,852	29,861	19,415
Income before income tax expense	(10,193)	(1,715)	(14,556)	(2,819)
Total assets	2,766,348	2,237,342	2,766,348	2,237,342
Total deposits	$ 36,752	$ 0	$ 36,752	$ 0